Switching device having contacts of two or more layers

ABSTRACT

A switching device having contacts with a coating consisting of at least two layers in which the inner layer having a thickness of at least 0.5 Mu m consists of metal having a melting point of more than 1800*C and provided with a layer having a thickness of 0.01 - 1 Mu m consisting of a metal having a melting point of less than 500*C and preferably provided with a layer of noble metal having a melting point of more than 1800*C with a thickness of 0.1 - 5 Mu m.

United States Patent Steinmetz et al.

[ June 10, 1975 SWITCHING DEVICE HAVING CONTACTS OF TWO OR MORE LAYERS lnventors: Anthony Steinmetz, Hilversum,

Netherlands; Hidde Walstra, Attleboro, Mass.

Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: May 3, 1974 Appl. No.2 466,713

Foreign Application Priority Data May 9, 1973 Netherlands ..7306445 US. Cl 200/268; 200/269 Int. Cl. l-10lh 1/02 Field of Search 200/267, 268, 269

References Cited UNITED STATES PATENTS 5/1972 Steinmetz et al. 200/268 X OTHER PUBLICATIONS Holms, Electrical Contacts Handbook, 1958, pp, 375-376.

Holms, Electrical Contacts, 1946, pp. 337-338.

Primary ExaminerRobert K. Schaefer Assistant ExaminerWilliam J. Smith Attorney, Agerzt, 0r Firm-Frank R. Trifari; Carl. P. Steinhauser [57] ABSTRACT 2 Claims, N0 Drawings SWITCHING DEVICE HAVING CONTACTS OF TWO OR MORE LAYERS The invention relates to a switching device ,having moving contacts.

Such devices using reed contacts in a miniaturized form in a hermetically closed envelope have in recent years been frequently used in modern telephone exchanges, computer systems and data transmission systems. In these switching devices the contact members generally at the ends of resilient conductors are jointly present in a closed space filled with a shield gas. The conductors consist of magnetic material by which the contact can be opened or closed with the aid of coils or permanent magnets placed outside the envelope.

Other embodiments of switching devices with contacts which are enveloped or not enveloped are relay or crossbar switches.

All these devices are subjected to very stringent re quirements as regards lifetime both in an unloaded and a loaded condition, while the contact resistance must be low and constant throughout the lifetime of the device.

A considerable improvement of the switching properties relative to the switching devices hiterto known has been achieved as is apparent from the U.K. Patent Specification 1,254,249 (US. Pat. No. 3,663,777 with contacts of which at least the contact surface is clad with a contact coating consisting of at least two layers of which the outer layer consists of metal having a thickness of 0.15 ,u.um while immediately or not immediately below this layer an interrupted or uninterrupted layer comprising at least 1.0 percent by volume of non-metal is present.

the outer layer preferably consists of a rare metal having a melting point of more than l800C such as ruthenium, rhodium, rhenium or osmium.

Very high lifetime qualities can be achieved with these contacts both in unloaded and loaded switching. A number of switching operations of l to 100 X can be realised without noticeable increase of the contact resistance.

A form of loaded switching often occurring is the socalled crosspoint load and the lifetest for this purpose is performed under a direct voltage of 50 Volt with cable discharges over 45, 75 and 140 ohm and with cable lengths of l, 10, 20 and 100 metres. The lifetime requirement is a number of switching operations of 0.5 3 X 10 dependent on the fact whether the cable must be discharged only once or must be discharged at each rebound.

Another form of load is the so-called logics load under a voltage of 12 Volt.

The invention provides a switching device with contacts of which at least the contact surface has a cladding, which device has an exceptionally long lifetime even under the difficult load conditions such as those that may occur during crosspoint load.

The switching device having a contact coating con sisting of at least two layers is characterized in that the inner layer having a thickness of at least 0.5 uum consists of a metal having a melting point of more than l800C on which an interrupted or uninterrupted layer having a thickness of 0.01 l gum is present consisting of a metal or a metal alloy having a melting point of less thant 500C.

A contact thus composed may be used as such, though only for those applications where the contact always switches under a tension.

According to a preferred embodiment a layer having a thickness of 0.5 5 ,uum consisting of noble metal having a melting point of more than l800C is present on the layer consisting of metal having a melting point of less than 500C. For the inner layer there applies that any metal having a melting point of more than l800C may be used, hence for example also molybdenum which due to oxidation is unsuitable for use as a possible outer layer. The thin intermediate layer having a melting point of less than 500C may consist of a Pb-Sn alloy, Bi, Woods metal, lead, tin etc. The layer need not be uninterrupted but may also consist of isolated aggregates having a coating of the surface up to at least 10 particles per sq.mm.

The switching properties of contacts in devices according to the invention are remarkably much better than has been considered possible up till now. The erosion of contacts is completely plane without a trace of peak and crater formation.

The techniques with which the layer combination according to the invention is provided are cathodic sputtering, vapour deposition and electrodeposition, but with a clear preference for the first-mentioned technique.

The invention will be further described with reference to the following exaples.

Reed contact whose part to be sealed within the envelope is approximately 7 mm long and 0.5 mm wide and which consist of magnetic nickel iron are successively coated in a conventional cathode sputtering device with a layer of Cu having a thickness of 0.5 num, a layer of Mo having a thickness of 2.0 num, a layer of a PbSn-alloy 1.1 percent by weight) having a thickness of0.0l [.LLIIII and finally a layer of Ru having a thickness of 0.1 uu. The argon pressure during sputtering is 10' mm Hg, the voltage is 1500 V, 1500 V, 800 V and 1500 V, respectively, and the current is 1A, 1.2A, 0.2A and 0.4A, respectively.

The reed contacts are subsequently pairwise sealed in a glass envelope and life-tested under the abovedefined crosspoint load. In all these cases lifetest values expressed in the number of switching operations were found from lto 10 X 10 without an increase of the contact resistance. The resistance in case of unloaded switching remains below 150 MOhm up to X 10 switching operations. Equivalent results are obtained when the PbSn layer is replaced by an equally thick layer of bismuth or by Woods metal (Bi 50 percent Cd 10 percent Pb 26.7 percent and Sn 13.3. percent).

When the ruthenium layer is not used and the outer layer thus consists of Pb-Sn, Bi or Wood's metal a contact coating is obtained whose resistance in case of unloaded switching increases to several dozen ohms. In case of loaded switching the result is slightly less than in the contacts having a ruthenium outer layer, but they amply satisfy the requirement of 0.5-3 X 10 switching operations being admissible without increasing the contact resistance.

What is claimed is:

1. A switching device having moving contacts of which at least the contact surface is clad with a contact coating which consists of at least two layers, characterized in that the inner layer having a thickness of at least 0.5 /,u.m of a metal having a melting point of more than terized in that a layer having a thickness of 0.1 -5 pm 5 p consisting of a noble metal having a melting point of more than l800C is present on the layer consisting of metal having a melting point of less than 500C.

0 mg? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,889,098 Dated June 10, 1975 0 Inventor) ANTHONY STEINMETZ ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 35, change "the" to read ---The-;

line 65, change "mum" to read um--; Col. 2, line 5, change "0.5 to read 0.l--; change "uum" to read -um-;

line 29, change "exaples" to read examples; f

0 line 34, change "uum" to read um;

line 35, change "uum" to read um;

line 36, change "1.1" to read --l:l-;

a line 38, change "uum" to read -um;

line 39, change uu" to read u--;

Col. 4, line 2, delete "5p".

' Signed and Sacaled this second Day Of September 1975 [SEAL] Arrest: T6

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummissimwr HfPalenIs and Trademarkx 

1. A SWITCHING DEVICE HAVING MOVING CONTACTS OF WHICH AT LEAST THE CONTACT SURFACE IS CLAD WITH A CONTACT COATING WHICH CONSISTS OF AT LEAST TWO LAYERS, CHARACTERIZED IN THAT THE INNER LAYER HAVING A THICKNESS OF AT LEAST 0.5 / UM OF A METAL HAVING A MELTING POINT OF MORE THAN 1800*C ON WHICH AN INTERRUPTED OR UNINTERRUPTED LAYER HAVING A THICKNESS OF 0.01-1/UM IS PRESENT WHICH LAYER CONSISTS OF A METAL OR A METAL ALLOY HAVING A MELTING POINT OF LESS THAN 500*C.
 2. A switching device as claimed in claim 1, characterized in that a layer having a thickness of 0.1 -5 Mu m 5 Mu consisting of a noble metal having a melting point of more than 1800*C is present on the layer consisting of metal having a melting point of less than 500*C. 